Welding control systems have taken numerous different forms. In general, some of these systems have involved measuring and controlling the weld energy applied to a workpiece. When the weld energy used deviates from a predetermined standard, means are employed to automatically correct the system.
In many welding systems, feedback networks are employed in which one or more welding parameters are measured and controlled. These parameters have included measurements and control of current, voltage or resistance. When deviations are detected from predetermined standards, the feedback network changes one or more of the welding parameters to bring them back to the standards being followed. Automatic control and mini-computer systems have also been employed in welding control.
Some welding control systems of the above types are described in U.S. Pat. Nos. 4,343,980; 4,101,753; 3,824,377 and 3,608,285.
In a resistance welding operation, the electrodes of a welding gun are closed to contact the workpiece which may involve two pieces to be welded together, as in a pair of panels in an automobile door, for example. The time taken to move the welding gun into contact with the workpiece is generally called "squeeze time". After the welding gun is in contact with the workpiece, the welding current is applied. The time that the welding current is applied is generally called "weld time". Following the weld current, the welding gun is held in contact with the workpiece for a predetermined time period to assure a good weld. This time is generally called "hold time". After the welding gun is removed from the workpieces, it is idle or off until the next welding operation. The time between welding operations is generally called "off time".
In welding some automotive parts, such as door panels, some operations are more critical than others because failure of the welds during use may cause injury to the driver or occupant of the automobile. In many cases, these critical welds are located at remote areas and not readily adaptable for an automatic welding operation and must be made manually.
Regardless of whether critical welds are made automatically or manually, the durations of the squeeze, weld, hold and off times provide information with respect to whether or not certain standards are being carried out in the welding operations. In addition to the quality of the welds involved, the times involved in performing the steps in a welding operation are important to a manufacturer to assure an efficient welding operation. For example, excessive times may greatly increase the costs involved. In some cases, this may also result in faulty welds. Short time durations less than the predetermined time standards may be indicative of a faulty weld. Thus measurements of times, currents and gun pressure alone may considerably simplify the welding control system involved. Also, the measurements of the times, weld currents and gun pressure may be readily recorded to facilitate corrections and locations of faults in the welding operation.